Internal combustion engines are well known to provide power for public and private transportation and other motorized applications. While some engine designs, such as the Wankel rotary engine, do not make use of pistons and cylinders, it is conventional in automobiles to use internal combustion engines with one or more piston-cylinder arrangements. The conventional reciprocating combustion engine uses a piston to compress a working fluid, such as gasoline, with air in a cylinder chamber. The mixture is then ignited by a spark and the resultant explosion drives the piston a fixed distance along the length of the cylinder. The energy generated by the ignition, and the subsequent linear movement of the piston, is transmitted through a piston rod, which is connected to a rotating crankshaft that provides output power, for example, to turn the wheels of an automobile.
The conventional internal combustion engine has been in existence for over a hundred years; in fact, as early as 1885, Daimler and Benz of Germany developed engines of this same type which are still being used in today's automobiles. Even though many improvements have been made throughout the years, the basic design of the internal combustion engine has remained relatively the same: A rigid block holds the cylinders, while the pistons go up and down a fixed distance via a heavy rigid crankshaft. Since the block is solid, the pistons travel up to a top point, as determined by the designer. The diameter of the pistons and the length of the stroke determine the displacement of air/vapor from the cylinder.
The designer decides in advance whether the engine is to run on regular or high-octane fuel. If regular fuel is chosen, the engine may be set to have a compression ratio of about 10:1 (stroke of 9-10 millimeters compresses air/vapor to 1 millimeter). For high-octane fuel and engines with ping sensors, the compression ratio is 12-14:1 (stroke of 12-14 millimeters compresses air/vapor to 1 millimeter). In general, a higher compression causes a more powerful explosion on the piston, thus giving the engine more power for the amount of fuel consumed.
The compression ratios are based on the engine running wide open—allowing maximum air/fuel vapor into the engine. However, when the engine is running at half power, the air/fuel vapor is reduced by half. The compression ratio drops by half because the engine is not fully charged. The engine that had a 9-10:1 compression ratio suddenly has only about a 4.5-5.0:1 compression ratio, and it is no longer operating at full efficiency. The power produced by a 4.5 -5.0:1 compression is generally not considered efficient.
Common automobile engine designs arrange the pistons and cylinders in a V-shape, in-line (straight), or in flat (boxer) patterns. A “V-6” engine, for example, is arranged with a bank of three cylinders at opposite sides of the engine, with each bank being at an oblique angle to the other. A multi-cylinder flat in-line engine has two opposed banks of cylinders, and a multi-cylinder in-line engine has all of the cylinders aligned in a single bank. Each configuration has somewhat different performance characteristics, form factors, and manufacturing complexities that may make it more suitable for certain vehicles.
Another type of piston-cylinder internal combustion engine, which is less common in the automotive industry, is the radial engine. As the name suggests, the radial engine design arranges the cylinders in a radial or angularly spaced circular pattern around the crankshaft. Typically, a “master” piston rod is fixed, or mounted by a non-pivoting link pin to the throw-piece, while the other “articulating” piston rods mount to the throw-piece by pivoting connections that allow them to rotate as the crankshaft and pistons move. The cylinder pattern gives the radial engine at least one distinct advantage over the other engine designs, and that is instead of using a long crankshaft with each piston moved by a different cam lobe, there is a single hub-like throw-piece to which all of the pistons connect.
Because of the radial engine's characteristic high power output, relatively low maximum engine speed allowing in some cases direct drive of the propeller without reduction gearing, and suitability for air-cooling instead of the weightier water-cooling process, radial engines have been historically used as airplane power plants. Today, radial engines in the airplane industry have largely been replaced by more common engine configurations or gas turbine engines, which are generally much lighter in weight.
Internal combustion engines of any design operate most efficiently when tuned to the load conditions applied to the engine. The cylinder count and size and the piston stroke are selected to provide an internal pressure and volumetric displacement corresponding to a particular output power. However, engine loading typically varies during operation, such as when changing speeds in an automobile, or when navigating steep terrain, or when towing a load. During times of engine operation when the output power is lower or higher than the load demands, the engine is operating inefficiently. Conventional engines are designed so that peak power and efficiency are available when the engine operates at full load. When conventional engines are operated at less than full load, less power is needed and, therefore, the power output is reduced by throttling back the air-fuel mixture, which reduces the pressure in the cylinders and increases the residual gas content following combustion, resulting in decreased operating efficiency. Such inefficiencies result in high fuel consumption and increased operating costs to the user.
Most engines are designed for maximum efficiency in the wide-open state. However, such a wide-open state is seldom the case during normal engine operation. At the wide-open setting, the engine receives the proper oxygen flow to ignite at the best pressure for the type of fuel being used. For example, suppose that a regular gasoline burns best when ignited at 150 pounds of pressure. The engine may use a compression ratio of 10:1. Inefficiencies will occur when the throttle is partly closed because less air goes into the cylinder, causing the optimum pressure of 150 pounds to suddenly drop, perhaps to only 75 pounds. Ignition still takes place, but not at its optimum level. Gas is still burned, but not efficiently, and economy is lost.
Trying to optimize the output power and efficiency of the engine over a wide range of operating conditions has been difficult to achieve in practice. Attempts to optimize performance characteristics for one operating condition often reduce the engine efficiency for other operating conditions. Hence, a need exists for an improved mechanical arrangement in an internal combustion engine that can compensate for varying operating conditions while maintaining peak efficiency at high or low output power.